Date: Wed, 22 May 2002 19:17:37 +0100 From: Doug Rabson <dfr@nlsystems.com> To: Alfred Perlstein <bright@mu.org>, "Dorr H. Clark" <dclark@applmath.scu.edu> Cc: freebsd-smp@FreeBSD.ORG Subject: Re: hyperthreading: myth or legend? (was Re: hyperthreading? (was Re: question)) Message-ID: <200205221917.37801.dfr@nlsystems.com> In-Reply-To: <20020522172759.GV54960@elvis.mu.org> References: <20020514222840.GB1585@elvis.mu.org> <Pine.GHP.4.21.0205220940410.28331-100000@hpux38.dc.engr.scu.edu> <20020522172759.GV54960@elvis.mu.org>
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On Wednesday 22 May 2002 6:27 pm, Alfred Perlstein wrote: > * Dorr H. Clark <dclark@applmath.scu.edu> [020522 09:58] wrote: > > I don't have access to a fancy Xeon, I just have > > a PIII dual-banger, so I'm relying on the list traffic. > > To summarize the past two months: > > > > On Thu, 14 Mar 2002, John Baldwin wrote: > > > > On Thu, 14 Mar 2002, Terry Lambert wrote: > > > > On Tue, 23 Apr 2002, FiberOps wrote: > > > > On Tue, 23 Apr 2002, John Baldwin wrote: > > > > On 23-Apr-2002 FiberOps wrote: > > > > This final message was not followed up except by me, > > although someone else informed me that while the CPUs > > launch, FreeBSD can't run processes on them. > > > > So I thought I'd try to stir up an answer to the original question: > > > > For the latest Xeon motherboards, does FreeBSD 4.x stable > > support hyperthreading? If not, does the current TOT? > > If not, why not? Is gcc an issue or not? If gcc is an issue, > > would this be an obstacle for all gcc-based OSes, > > not just FreeBSD, most prominently among these Linux? > > > > Clear answers gratefully appreciated, > > I'm glad you chose to take the word of a couple of people > that have never used a hyperthreading board above what I've > already told you. > > Here's what I know: > The additional CPUs probe. > > A benchmarking utility reports equivelant performance to a 4 way > machine. One thing we don't do which we could use to squeeze extra performance is = to=20 adjust the allocation of cpus to procs. When one hyperthread is idle on a= cpu=20 while the other one is running, the running hyperthread is faster since i= t=20 can use more functional units. When we schedule a new thread, we should=20 prefer cpus which are totally idle (i.e. both hyperthreads are idle) and = only=20 schedule two hyperthreads on a single cpu when there is no totally idle c= pu=20 left. --=20 Doug Rabson=09=09=09=09Mail: dfr@nlsystems.com =09=09=09=09=09Phone: +44 20 8348 6160 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-smp" in the body of the message
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